fix(cli): resolve duplicate 'skills' subparser crash on Python 3.11+

Fixes #898 — Python 3.11 changed argparse to raise an exception on
duplicate subparser names (CPython #94331). The 'skills' name was
registered twice: once for Skills Hub and once for skills config.

Changes:
- Remove duplicate 'skills' subparser registration
- Add 'config' as a sub-action under the existing 'hermes skills' command
- Route 'hermes skills config' to skills_config module
- Add regression test to catch future duplicates

Migration: 'hermes skills' (config) is now 'hermes skills config'

tests/hermes_cli/test_skills_subparser.py

@@ -0,0 +1,35 @@
+"""Test that skills subparser doesn't conflict (regression test for #898)."""
+
+import argparse
+
+
+def test_no_duplicate_skills_subparser():
+    """Ensure 'skills' subparser is only registered once to avoid Python 3.11+ crash.
+
+    Python 3.11 changed argparse to raise an exception on duplicate subparser
+    names instead of silently overwriting (see CPython #94331).
+
+    This test will fail with:
+        argparse.ArgumentError: argument command: conflicting subparser: skills
+
+    if the duplicate 'skills' registration is reintroduced.
+    """
+    # Force fresh import of the module where parser is constructed
+    # If there are duplicate 'skills' subparsers, this import will raise
+    # argparse.ArgumentError at module load time
+    import importlib
+    import sys
+
+    # Remove cached module if present
+    if 'hermes_cli.main' in sys.modules:
+        del sys.modules['hermes_cli.main']
+
+    try:
+        import hermes_cli.main  # noqa: F401
+    except argparse.ArgumentError as e:
+        if "conflicting subparser" in str(e):
+            raise AssertionError(
+                f"Duplicate subparser detected: {e}. "
+                "See issue #898 for details."
+            ) from e
+        raise